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Analyses of the spatial distribution pattern, spatial genetic structure and of genetic diversity were carried out in two tropical tree species with contrasting breeding systems and different ploidy levels using a 50-ha demographic plot in a lowland dipterocarp forest in Peninsular Malaysia. Shorea leprosula is a diploid and predominantly outcrossed species, whereas S. ovalis ssp. sericea is an autotetraploid species with apomictic mode of reproduction. Genetic diversity parameters estimated for S. leprosula using microsatellite were consistently higher than using allozyme. In comparisons with S. leprosula and other tropical tree species, S. ovalis ssp. sericea also displayed relatively high levels of genetic diversity. This might be explained by the lower pressure of genetic drift due to tetrasomic inheritance, and for autotetraploids each locus can accommodate up to four different alleles and this allows maintenance of more alleles at individual loci. The observed high levels of genetic diversity in S. ovalis ssp. sericea can also be due to a random retention of more heterogeneous individuals in the past, and the apomictic mode of reproduction might be an evolutionary strategy, which allows the species to maintain high levels of genetic diversity. The spatial distribution pattern analyses of both species showed significant levels of aggregation at small and medium but random distribution at the big diameter-class. The decrease in magnitude of spatial aggregation from small- to large-diameter classes might be due to compensatory mortality during recruitment and survival under competitive thinning process. Spatial genetic structure analyses for both species revealed significant spatial genetic structure for short distances in all the three diameter-classes. The magnitude of spatial genetic structure in both species was observed to be decreasing from smaller- to larger-diameter classes. The high spatial genetic structuring observed in S. ovalis ssp. sericea at the small-diameter class is due primarily to limited seed dispersal and apomictic mode of reproduction. The similar observation in S. leprosula, however, can be explained by limited seed and pollen dispersal, which supports further the fact that the species is pollinated by weak fliers, mainly of Thrips and Megalurothrips in the lowland dipterocarp forest. [ABSTRACT FROM AUTHOR]

Explores the breeding system and seed dispersal in Shorea leprosula in Malaysia. Conduction of microsatellite analysis of embryos and immature and mature fruits fallen in litter traps; Mean outcrossing rate of mature fruit; Elements of postpollination selection against inbreeding.

The development of mycorrhizal infection on seedlings of the dipterocarp, Shorea leprosula (Miq.), was followed for 7 months after germination at three sites in West Malaysia. Arbuscular mycorrhizal infection was riot observed. Seedling roots had well-developed ectomycorrhizal sheaths, but no Hartig net, 20 d after germination, i.e. before the leaves had formed. By 2 months a range of ectomycorrhizal types with well-developed Hartig nets were present. Twenty-three types were recognized, of which 15 were common to all three sites, and 20 to two sites. Individual seedlings never had more than five types and normally had one or two types only. The majority of ectomycorrhizas were formed by relatively few fungi and the six most abundant types at each site accounted for 77-92% of the mycorrhizas. On the basis of the frequency of types (i.e. number of seedlings having mycorrhizas of a given type), and the number of times that a type contributed more than 40% of the mycorrhizas on a given seedling it was possible to recognize group of 12 dominant types. At each site new types were encountered at each harvest, and the number of types per harvest also increased. As well as fungi entering the mycorrhizal community as time progressed there was clear evidence that some fungi were lost or declined in relative abundance. Over the study period the level of infection fell at the two sites at which it was initially greatest. Although the community of mycorrhizal fungi was broadly similar at all three sites, overall level of infection, total number of types and number of types per seedling were highest at the site which appeared to have experienced the least disturbance and at which there were the greatest number of adult S. leprosula trees. [ABSTRACT FROM AUTHOR]

Masting, the production of large seed crops at intervals of several years, is a reproductive adaptation displayed by many tree species. The predator satiation hypothesis predicts that starvation of seed predators between mast years and satiation during mast years decreases seed predation and thus enhances tree regeneration. Mast fruiting comes at demographic costs such as missed reproduction opportunities and increased density-dependence of recruits, but it remains unknown if predator satiation constitutes a sufficiently large benefit for masting to evolve as a viable life-history strategy. So far, no studies have quantified the net fitness consequences of masting. Using a long-term demographic data set of the dipterocarp Shorea leprosula in a Malaysian forest, we constructed stochastic matrix population models and performed a demographic cost-benefit analysis. For observed values of mast frequency and seed predation rates, we show that strict masting strongly increases fitness compared with fruiting annually. Model results also show that the demographic costs of mast fruiting are very low compared to the demographic losses due to seed predation in a scenario of annual fruiting. Finally, we find that mast fruiting would still be selected for even at low levels of seed predation and when including additional costs such as decreased adult growth rates, limiting crop size and density-dependent seedling survival. Synthesis. Our results are consistent with the predictions of the predator satiation hypothesis: mast fruiting increases fitness for a range of seed predation levels. Under seed predation pressure annually fruiting species are at a strong disadvantage and as a result a mast fruiting strategy may swiftly confer a fitness advantage. Our study shows that demographic modelling allows the weighing of fitness benefits and costs of life-history phenomena such as strict masting. [ABSTRACT FROM AUTHOR]